1. Field of the Invention
This invention relates to a light modulation element for changing the position of a moving grid by an electrostatic force for executing light modulation, an array-type light modulation element, and a flat-panel display unit.
2. Description of the Related Art
A light modulation element is available for controlling the amplitude (strength), phase, travel direction, etc., of incident light for processing and displaying an image, pattern data, etc. With the light modulation element, the refractive index of a substance allowing light to pass through is changed by the outer field applied to the substance and finally the strength of light passing through or reflecting on the substance is controlled through optical phenomena such as refraction, diffraction, absorption, dispersion, etc. One of the light modulation elements is a liquid crystal light modulation element using the electro-optic effect of liquid crystal. The liquid crystal light modulation element preferably is used with a liquid crystal display of a thin flat-panel display unit.
The liquid crystal display has a structure wherein nematic liquid crystal oriented in parallel with substrates forming a pair of conductive transparent films and twisted 90 degrees between the substrates is placed between the substrates and is sealed, then sandwiched between perpendicular deflecting plates. The liquid crystal display produces display using the fact that the liquid crystal molecules are oriented in the long axis direction perpendicular to the substrate by applying a voltage to the conductive transparent film and the transmission factor of light from a backlight. An active-matrix liquid crystal panel using TFTs (thin-film transistors) is used to provide the liquid crystal display with good responsivity to a moving image.
A plasma display has a structure wherein a large number of electrodes in a perpendicular direction arranged regularly corresponding to discharge electrodes are placed between two glass plates sealed with rare gas of neon, helium, xenon, etc., and the intersecting points of the counter electrodes are used as unit pixels.
The plasma display produces display by selectively applying a voltage to the counter electrode specifying each intersecting point based on image information for causing the intersecting point to discharge and emit light and exciting phosphor for emitting light by generated ultraviolet rays.
FED has a structure wherein a pair of panels is placed facing each other with a minute spacing between and a flat display tube for sealing the surroundings of the panels is provided. The panel on the display surface side is formed on the inner face with a fluorescent film and field emission cathodes are arranged in a one-to-one correspondence with unit light emission areas on the rear panel. A typical field emission cathode has a field emission type microcathode like a drill projection called an emitter tip of minute size.
The FED produces display by using the emitter tip to take out an electron and accelerating and applying the electron to a phosphor for exciting the phosphor.
However, the flat-panel display units in the related arts described above involve the following various problems:
In the liquid crystal display, light from the backlight is allowed to pass through multiple layers of the deflecting plates, the transparent electrodes, and color filter, thus the light use efficiency lowers. The high-grade liquid crystal display requires that TFTs and liquid crystal must be sealed between two substrates and be oriented, thus it is difficult to provide a large area. This is a disadvantage of the liquid crystal display. Further, since light is allowed to pass through the oriented liquid crystal molecules, the viewing angle becomes narrow. This is another disadvantage of the liquid crystal display.
In the plasma display, partition formation for generating plasma for each pixel results in an increase in manufacturing costs and large weight. This is a disadvantage of the plasma display. A large number of electrodes corresponding to discharge electrodes must be arranged regularly for each unit pixel. Thus, as the definition becomes high, the discharge efficiency lowers and the light emission efficiency of the phosphor by vacuum ultraviolet ray excitation is low, thus it is hard to provide a high-definition, high-brightness image in high power efficiency. This is another disadvantage of the plasma display. Further, the drive voltage is high and a drive IC is expensive. This is also a disadvantage of the plasma display.
In the FED, ultrahigh vacuum needs to be produced in the panel to make discharge highly efficient and stable, and the manufacturing costs increase as with the plasma display. This is a disadvantage of the FED. Since field emission electron is accelerated and applied to the phosphor, high voltage becomes necessary. This is also a disadvantage of the FED.